Just last month our group at the Northeastern Eye Institute confirmed another case of Acanthamoeba keratitis. Although the patient received an early diagnosis, he is still likely to experience significant morbidity and much anxiety associated with having this frightening condition. In fact, Acanthamoeba continues to have a relatively low attack rate with substantial geographic and seasonal differences.

Incidence rates range from one to 33 cases per million contact lens wearers, with a higher number of reported cases occurring during the summer months.^1-3 Scotland and South Korea report the highest national rates._⁴

The Disease
Although Acanthamoeba keratitis is an exceedingly rare infection, you may still find yourself facing such a case. Keep in mind that a timely diagnosis is crucial for the best outcome. Patients with Acanthamoeba keratitis often present with an early non-specific keratitis that progresses over time. Variable symptoms include eye pain, redness, blurred vision, light sensitivity and tearing. Epithelial signs include patchy involvement and a stellate or pleomorphic epitheliopathy.⁴ Punctate erosion, an elevated dendritiform and a “bull’s eye” lesion are possible. Stromal involvement can include a granulomatous, nonsuppurative infiltrate and radial neuritis. Ring infiltrates appear later and are not pathognomonic for Acanthamoeba infection.⁴ Note: Any non-specific keratitis thought to be bacterial or viral that doesn’t display a seemingly appropriate response to therapy should be reconsidered for rare diseases such as fungal and protozoan infections.

Today’s Research
Two recently released studies take a close look at multi-state outbreaks, from 2008 through 2011, following the recall of a multipurpose disinfecting solution in 2007.^1,2 Experts anticipated that the rates of Acanthamoeba keratitis would fall significantly after the solution recall. Instead, a convenience sample with surveillance data collected from 13 U.S. ophthalmology centers and laboratories showed that Acanthamoeba keratitis cases remained higher than pre-launch levels.^1,2

Practitioners should be vigilant in diagnosing and treating Acanthamoeba keratitis.

Surveillance monitoring of compounding pharmacies reported an increase in anti-amoebic medications ordered during the post-solution recall phase, which correlates with the data collected at the abovementioned sentinel sites.¹ Unlike the Fusarium outbreak, where the rates declined dramatically following a solution recall, the cases of Acanthamoeba keratitis did not rapidly decrease after the implicated solution was recalled. Remember, a recalled product is not always “unsafe” and it’s crucial to continue to follow trends and set new baselines following any recall. Of particular note, heightened awareness and additional diagnostic techniques do not fully explain the persistent levels of new cases detected in the past few years.^1,2

Risk Factors
Risk factors for Acanthamoeba keratitis include contact lens wear, a significant microdehiscence, repeated inoculation with contaminated solution or water, and host susceptibility.4 According to the CDC, multiple contact lens hygiene practices are associated with increased risk for infection, including:
• Topping-off contact lens solutions in case (4.54).²
• Recent contact lens wear (3.22).²
• Storing contact lenses in water (5.37).²
• Handling contact lenses with wet hands (2.17).²

Coupled with the valuable data obtained from previous studies, practitioners can help prevent infection by identifying additional risks and encouraging their patients to engage in recommended hygienic practices.^1,2

High-risk behavior includes:
• Showering while wearing lenses more than five times a month (9.07).^1,5
• Reusing solution (3.17).⁵
• Failing to rub lenses at least 10 times per month (9.05).⁵
• Failing to replace lens storage cases every three months (2.79).⁵

Concerted efforts to prevent this dreaded disease are critical. Reducing the number of cases of Acanthamoeba keratitis is dependent on practitioners having a better understanding of the disease process, consistently educating patients on the risks and reducing overall exposure. Continued research will help us further understand the disease process and help shape prevention efforts. In the meantime, our best defense is to actively and consistently educate our patients.

The stakes are high. The public has a low tolerance for rare conditions, and patients are counting on you to teach them how to avoid risky contact lens care practices. As a practitioner, the best thing you can do is pay close attention to your patients and don’t hesitate to provide gentle reminders.   

1. Yoder JS, Verani J, Heidman N, et al. Acanthamoeba keratitis: The persistence of cases following a multistate outbreak. Ophthalmic Epidemiology. 2012 Aug;19(4), 221-5.
2. Brown AC, Ross J, Yoder J, et al. Elevated Acanthamoeba keratitis incidence despite a 2007 outbreak associated product recall: a multi-state investigation (2008-2011). Presentation at the annual Epidemic Intelligence conference, April 16-20, 2012; Atlanta.
3. Stockman LJ, Wright CJ, Visvesvara GS, et al. Prevalence of Acanthamoeba spp. and other free-living amoeba in household water, Ohio, USA 1990-1992. Parasitol Res. 2011 Mar;108(3):621-7.
4. Byrne J. Acanthamoeba keratitis incidence increases in some areas. Primary Care Optometry News. 2006 Sep. Available at: www.healio.com/optometry/cornea-external-disease/news/print/primary-care-optometry-news/%7B67ef49c9-dfa2-4f1f-9c6d-6e15e5497dcd%7D/acanthamoeba-keratitis-incidence-increases-in-some-areas. Accessed October 2012.
5. Joslin CE, Tu EY, Shoff ME, et al. The association of contact lens solution use and Acanthamoeba keratitis. Am J Ophthalmol. 2007 Aug;144(2):169-80.